Over the last few years, there has been a tremendous growth in the use of multiple-beam antenna systems for satellite communications. For example, multiple-beam antennas are currently being used for direct-broadcast satellites (DBS), personal communication satellites (PCS), military communication satellites, and high-speed Internet applications. These antennas provide mostly contiguous coverage over a specified field of view on Earth by using high-gain multiple spot beams for downlink (satellite-to-ground) and uplink (ground-to-satellite) coverage.
Conventional multiple-beam satellite payloads employ separate uplink and downlink antenna suites. For example, the Anik-F2 satellite uses 5 uplink antennas in one antenna suite and 5 downlink antennas in another antenna suite, requiring 10 apertures. In addition, twice the number of feed horns is required. This is due to the lack of thin-walled feed horn that could efficiently support both uplink and downlink frequencies that are widely separated. Each feed horn in the downlink antenna suit is capable of providing signal transmission over a selected transmission frequency band, whereas each feed horn in the uplink antenna suit is configured to provide signal reception over a required reception frequency band. These conventional multibeam satellites require several antenna apertures limiting the available real estate on the spacecraft for other payload antennas and are relatively expensive due to twice the number of reflectors and twice the number of feed horns required when compared to the dual-band antenna system disclosed herein. Other conventional multiple-beam satellite payloads, such as AMC-15, AMC-16 and Rainbow, employ dual-band antennas using low-efficiency corrugated feed horns to realize dual-band operation, but have a significantly lower RF performance.
Therefore, there is a need to provide multiple spot beam coverage at both uplink and downlink frequency bands using dual-band feed horns with each horn forming congruent beams at both uplink and downlink frequency bands. That means that the horn needs to cover frequency bands that are widely separated, for example, 20 GHz and 30 GHz frequency bands. In addition, it is desirable to provide high horn efficiency, e.g. higher than 80%, at both frequency bands in order to (a) reduce the spillover losses, (b) improve the coverage gain and (c) improve the copolar isolation among beams that reuse the same frequency channels.